The present invention concerns a method and an apparatus for impregnating a continuous fiber bundle. The method and the apparatus of the invention are appropriate for impregnating fiber bundles with molten or fluid resin in manufacturing fiber-reinforced materials consisting of a reinforced fiber bundle or fiber bundles bound with a thermoplastic resin material which forms a matrix.
The greatest problem related to manufacturing such products is the viscosity of certain materials included in the matrix resin. Since individual fibers in fiber bundles lie very close to one another, it is difficult to effectuate the resin material penetration into a resin bundle and its surrounding of all individual fibers. This is however, indispensable considering the desired properties of the product, such as strength, rigidity, chemical durability, further processability, etc.
Endeavors have been made to develop a number of solutions to the problem. In one method, fiber bundles are conveyed through a so-called crosshead die, in which molten or liquid resin is made to enter into fiber bundles travelling through the nozzle chamber at elevated pressure. The crosshead-die procedure has proved inefficient in impregnating fiber bundles with thermoplastic resin because not all individual fibers get surrounded with resin although during the absorption phase the fibers are kept at elevated pressure. For impregnating reinforcing fibers, the range of viscosity of resin 1 to 10 PaS would be desirable, the typical order of magnitude being 10.sup.2 PaS, and in some cases, the order of magnitude 10.sup.3 PaS being acceptable. However, a typical range of viscosity for molten thermoplastic resins is 10.sup.2 to 10.sup.6 PaS order of magnitude; it is thus obvious that with the crosshead die procedure surrounding all individual fibers with resin is extremely difficult if not impossible.